Ask a friend.

Other people — strangers, even — have an uncanny ability to detect when something's not right in someone else's relationship.

BYU psychologists tested out this idea by having couples draw an object together, with one participant blindfolded and the other one giving instructions on what to draw. The whole thing was videotaped. Before they started, the scientists had the couples answer a few questions about their relationship in private, including whether or not they'd ever cheated.

Then, the researchers had a group of strangers watch the footage and guess which couples included a partner who'd ever cheated. The volunteers were surprisingly accurate.

Although preliminary, the research suggests that, simply by watching a couple doing something that requires working together, an outside observer may be able to detect infidelity or unhappiness.

"People make remarkably accurate judgments about others in a variety of situations after just a brief exposure to their behavior," the researchers wrote in the study.

"These findings suggest that the human mind is not unfit to distinguish between truth and deception," write the researchers in the study, "but that this ability resides in previously overlooked processes."

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Listen carefully to the words they use.

For a recent study, University of Texas at Austin professor of psychology James W. Pennebaker looked at some data he and his colleague Diane Berry had gathered from a text analysis program. They found that some specific patterns of language were helpful at predicting when someone was avoiding the truth.

Liars, they found, tended to use fewer of the following three types of words:

In his study, University of Missouri researcher Russell Clayton studied the social media habits of close to 600 Twitter users. Most people used Twitter for roughly an hour a day, 5 days a week. But those who used it more often than that were more likely to get in arguments with their partners, get divorced, or cheat. The more time they spent on Twitter, the worse the relationship outcomes were.

It's unlikely that too much tweeting, posting, and liking caused other people to cheat, of course, but if anything the study showed that there's certainly a connection between the two.

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Watch for sudden changes in behavior.

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If you've been with your significant other for a while, chances are you know how they normally act — what type of foods they eat, how they react to challenges or surprises, how well they listen, and so on.